This invention relates in general to facsimile systems and, in particular, it relates to a signalling method for use in such systems whereby one machine may direct an unattended remote machine to transmit documents to a near side machine.
In facsimile systems, in the most common mode of operation, a calling party's unit transmits documents to the called party's unit. However, it is also desirable to provide a feature whereby the calling party's unit may direct an unattended called party's unit to transmit a document or documents from it to the calling party's unit. This capability is especially desirable in units having automatic paper feed, since in these machines documents may be loaded into a paper tray, and the unit may then be left unattended. Thereafter, a caller may contact the unattended unit and direct it to transmit the waiting documents.
In one such known prior art unit, a signalling method is employed which allows for the aforementioned capability. In this prior art method, before a handshake has been exchanged between the respective machines, the calling party's unit directs a continuous tone which, when received by the called party, indicates to it that it is to respond by transmitting documents rather than by receiving them.
This prior art signalling method suffers from a number of disadvantages. First, recommended signalling procedures have been proposed by the CCITT and these procedures are increasingly being used as international signalling standards for facsimile systems. The use of a continuous tone, such as that employed by the known prior art, is incompatible with these standards. It would be desirable to provide a signalling method for directing a remote facsimile unit to transmit documents rather than to receive them which would not be incompatible with the recommendations of the CCITT.
Another disadvantage of the prior art technique of using a continuous tone is that during the period in which the continuous tone is directed from the calling party to the called party, no other information between the units may be exchanged. It would be desirable to provide a signalling method which would increase the amount of information transmitted in any given time so as to make full use of relatively expensive long distance telephone time. In accordance wwith the present invention, a signalling method is provided whereby a calling party may direct a remote, unattended unit to transmit a document or documents to it without the above noted disadvantages.